Radio receiver



Jan. 6, 1942.

E. F. ANDREWS RADIO RECEIVER Original Filed April 8, 1933 ,5Sheets-Sheet 2 INVENTOR. (Fizz/4m? (If Q'r/drez/s ATTORNEYS Jan. 6,1942. E. F. ANDREWS RADIO RECEIVER 5 Sheets-Sheet 3 Original Filed April8, 19:53

62! JIg/ENTOR.

lad, 71 719% By M ATTORNEYS Jan. 6, 1942.

RADIO RECEIVER Original Filed April 8, 1933 5 Sheets-Sheet 4 E. F.ANDREWS 2,269,300 I 5 Sheets-Sheet 5 E. F. ANDREWS RADIO RECEIVEROriginal Filed April 8, i933 Jhn.6,1942;

. 6 If)? w [IL ilmmu 33 Patented Jan. 6, 1942 RADIO RECEIVER Edward F.Andrews, Chicago, Ill., assignor to Radio Corporation of America, NewYork, N. Y., a corporation of Delaware Application January 9, 1939,Serial No. 249,908, now Patent No. 2,218,501, dated October 22, 1940,which is a division of application April 8,

1933, Serial N0.

665,074, now Patent No.

2,143,532, dated January 10, 1939. Divided and this application July 1,1939, Serial No. 282,401

13 Claims.

This application is a divisional from my copending application SerialNo. 249,908, filed January 9, 1939, Patent No. 2,218,501 dated October22, 1940, which is a divisional from my application Serial No. 665,074,filed April 8, 1933, Patent No. 2,143,532, dated January 10, 1939.

This invention relates to radio receivers and has for one of its objectsthe provision of an improved radio receiver.

A further object of the invention is to provide an improved radioreceiver particularly adapted for use in an automobile or elsewhere withlow voltage current.

A further object of the invention is to provide, in a radio receiverincluding an interrupter, means for preventing high frequencydisturbances occasioned by the interrupter from being amplified by thetubes of the receiver so as to cause undesired noises in the loudspeaker.

A further object of the invention is to provide a radio receiver havingits elements mounted on a grounded base, and comprising a built-in powersupply mounted on the base, said supply including an interrupter andassociated coils related to the grounded base so as to suppress in anadvantageous manner the high frequency disturbances created by theinterrupter.

Other objects, advantages, and capabilities of my invention will appearfrom the following description of preferred embodiments thereof,

taken in conjunction with the accompanying drawings, in which:

Fig. 1 is a wiring diagram of one embodiment of the invention;

Fig. 2 is a wiring diagram of a further embodiment of the invention;

Fig. 3 is an illustration of a radio set embodying the invention, themain unit being shown in plan with its cover partly broken away and theremote control unit being shown in sectional elevation;

Fig. 4 is an end view of the remote control unit, with its cover partlybroken away;

Fig. 5 is an elevation of the main unit, the cover being shown insection in order to display elements normally obscured thereby;

Figs. 6, '7, 8 and 9 are fragmentary wiring diagrams illustrating themeans for preventing excessive attenuation of signal energy whentransmitted from one unit to the other, and

Fig. 10 is a wiring diagram of a still further embodiment of theinvention.

Referring more particularly to Fig. 3, it is to be noted that the mainunit, which is designated by the reference numeral 10, is substantiallysimilar in general structure to the radio receiver described and claimedin Patent 2,103,135, issued December 21, 1937. This main unit is alsoshown in Fig. 5 and comprises a base H which may be of inverted dishshape provided with an outwardly projecting flange 12 to which issecured a closure plate I3. The space between the upper face of the baseH and the closure plate 13 provides accommodation for wiring and smallradio parts. A block 14 is mounted in the center of the base H to serveas a support for the pot 15 of a loud speaker IS. The loud speaker ispreferably of the dynamic cone type, the cone I! being directed upwardlyas shown in Fig. 5. A cover I8 is supported upon the speaker, forexample, by means of screws I9 which secure it to the edge of thespeaker frame adjacent the periphery of the cone.

The central portion of the cover I8 is provided with openings for theegress of sound from the speaker. The cover I8 is preferably of inverteddish shape and it extends downwardly towards the base H. The lowestportion of the cover I8 is of diameter somewhat larger than the base Hso as to provide an annular opening 2| for the egress of sound wavesfrom the lower side of the speaker cone. The base H serves to provide amounting for radio apparatus such as radio tubes, transformers, avibrator and the like, which will hereinafter be described in greaterdetail. Such radio apparatus is located in a ring around the pot 15 ofthe loud speaker, being located within the annular space between theloud speaker and the cover l8. It will readily be understood that suchradio apparatus may be rendered available for adjustment, replacementand the like, by merely removing the cover l8, which may be done bytaking out the screws l9.

Owing to the fact that it is preferred to tune the receiver in theremote control unit, it is not necessary to mount a variable condenserin the main unit as in the case of the aforesaid patent. The remainingradio apparatus is more convenient to this manner of assembly and thedimensions of the main unit may be somewhat reduced.

Energy is supplied to the main unit In by a cable 22. For a setemploying the wiring diagram of Fig. 1, this cable comprises a conductor23 and a conductive shield 24, insulated from each other by suitableinsulation. The conductor 23 and shield 24 are connected to a battery 25in the manner shown in Fig. 1. The main unit 10 is connected to theremote control unit 26 by means of a flexible cable 21 of suitablelength. The number and relation of conductors which is enclosed anelectro-magnet 85 which controls points 88 in series with the winding ofsaid magnet so as to cause continual interruption in the current flowingthrough the primary of the transformer 15. A condenser 81 and highresistance 88 are provided both across the winding 85 and points 85. Theconductor 8| is also connected to the field winding of the speaker I6,

the other end of this winding being grounded.

The continual interruption of the fiow of current through the contacts86 develops undesired high frequency disturbances. It is important,particularly where an interrupter power supply is made a part of theradio receiver, to isolate these high frequency disturbances and toprevent them from being amplified by the tubes of the receiver so thatthey appear as objectionable noises in the speaker output. To isolatethese disturbances, one of the contacts 86 and the metal shield 14around the interrupter are grounded to the metal base which serves as acommon ground for the receiver and the power supply, and on which theinterrupter, transformer, tubes, and other elements are mounted. Thegrounding of one side of the circuit in this manner tends to reduce to aminimum the potential differences between the various parts connectedthereto. Thus, there is relatively little tendency for the undesiredhigh frequency disturbances to reach the tubes through the grounded sideof the circuit. The interrupter coil 85 and the primary of thetransformer 15 are interposed between the ungrounded contact 86, at thesource of the undesired disturbances, and the various conductorsconnected to the ungrounded side of the circuit from which the undesiredhigh frequency disturbances might be radiated to the tubes, or throughwhich the disturbances might be carried to the tubes by conduction. Theinductance of these coils presents a high impedance to the passage ofthese high frequency disturbances. The condenser 81, which bridges fromthe connected ends of the coil 85 and the primary of the transformer 15to ground, forms a low impedance path to ground tending to shortcircuitthat portion of the undesired high frequency disturbances which may passthrough the coil 85. Thus, by connecting one of the contacts 86 directlyto the common ground, the coil 85, the condenser 81, and the primary ofthe transformer 15 form a filter effective for isolating the undesireddisturbances from the ungrounded side of the circuit through which theywould otherwise be transmitted to the tubes. It is preferred to locateone or more of the inductances constituting the filter for undesiredcomponents adjacent the interrupter points and to shield the interruptercontacts and adjacent portions of the interrupter circuit, including allor part of the inductances and the condenser forming the high frequencyfilter, with grounded shielding means.

It will, of course, be understood that all the grounds indicated in theupper part of Fig. 1, which corresponds to the main unit, are made tothe common base II. The ungrounded sides of the tube filaments areconnected to the line 8!, the filament of tube 28 being connectedthereto by line 65 of cable 21, and the filament of tube 15 beingconnected thereto by line 82. Choke coils 9| are provided in thefilament current circuit, being preferably arranged in series in thefilament supply circuit, serving with the filament resistances toprovide an induction-resistance filter which effectively filters outhigh frequency disturbances produced by the vibrator 14 and which maynot be completely isolated by the means above described. This filter,including the choke coils 91, is also effective in preventing undesiredhigh frequency disturbances originating in the ignition or batterycharging system of the automobile from reaching the tubes. It will beseen that the filtering effect is greatest towards the input end of thereceiving set, where any disturbance present would be amplified to thegreatest extent.

The choke coil 92 is connected in series with the lead which suppliesplate current to the tube 28. This choke coil prevents oscillation whichmight be caused by disturbances passing through lead 55, coil 53 and theplate ground capacity of the tube 28.

It is preferred that the rectifying tube 18 passes current when thepoints 86 make contact, rather than when they break contact. The changefrom one condition to the other may be effected in many ways, one waybeing to reverse the connections of the secondary winding of thetransformer 15. The set can thus be readily adapted for any automobile,regardless of which pole of the battery is grounded.

The operation is as follows: The switch 38 being closed, the circuitsthrough the filaments are made, likewise the circuit through thevibrator or interrupter 14, so that an interrupted current passesthrough the primary of the transformer 15. The voltage of this currentis stepped up in the secondary of the transformer and is rectified intube 16 so as to provide B voltage by means of conductor 19. The fieldwinding of the speaker I6 is energized and the desired station can betuned in by actuating the gang of condensers 29. The volume levelcontrol 63 adjusts the relative grid bias of tube 4! by making thecathode more or less positive. It is to be noted that this control inthe main unit is effected from the control unit by variation of a directcurrent which is of practically constant value for any particular manualsetting of the volume level control 63.

The automatic volume control voltage is applied to the grids of thetubes 39 and 40, which elements are ahead of the source of energy fromwhich the automatic volume control voltage is derived, which source isthe plate circuit of the tube 4|]. Automatic volume control voltage isalso a plied to the grid of the tube 4|, which. is after the source ofthe energy which supplies the automatic volume control voltage which. ashas been noted, is the plate of the tube Ml. It may here be pointed outthat the effective automatic volume control voltage applied to the tubesbefore the source of the automatic volume control energy is to decreasethe gain of these tubes, and hence the automatic volume control voltageproduced, so that these tubes provide only a diminishing correctiveeffect. However, the application of automatic volume control voltage tothe grid of a tube after the source of automatic volume control energy,such as tube 4! produces a reduction of gain without any reduction ofthe automatic volume control voltage. By tapping in the grid connectionof the tube M at a suitable point on the resistor H, signals ofsubstantially uniform strength can be obtained from divers stations withantenna signals of widely different power. Indeed, by suitableadjustment of the connection of the grid 4| to the resistor II, it ispossible to make a stronger antenna signal appear as a Y the seconddetector.

weaker audible signal than that derived from a weaker antenna signal.

The embodiment of the invention diagrammatically shown in Fig. 2 islargely similar to that shown in Fig. 1 and similar reference numeralsare employed to designate similar parts. In this embodiment the antennalead 45 is conveyed through the cable 21 within a grounded metal shield93, for the purpose of preventing the antenna lead 46 from picking upelectrical disturbances.

In this embodiment the tube 42 is dispensed with and the tube 43fulfills the functions of the tubes 42 and 43 in the embodiment ofFig. 1. This tube 43 contains two diodes and triode in the sameenvelope, all having a common cathode. One diode plate 94 serves as asecond detector, the other diode plate 95 serves as a source ofautomatic volume control potential which is applied to the grids oftubes 39 and 40, a portion thereof being applied to the grid of tube 4|,as in the previously described embodiment.

The triode elements of tube 43 act to amplify the output of the diodeconstituted by plate 94 and the cathode at audio frequency. The detectedsignal appears across the resistance 95 and is impressed upon the gridof the tube 43 through the filter resistor 91 and the capacity 98. As inthe previously described embodiment, the tuned intermediate frequencytransformer 99 connected to the plate of the tube 40 steps down theoutput of that tube and feeds a signal of reduced amplitude to the gridof the tube 4| by means of the winding I00. This winding is here showntuned to the intermediate frequency.

by taking practically all the gain in the first intermediate frequencytubes, substantially the maximum gain is available in the plate circuitof the tube 40, which is the source of automatic volume control energy.Any gain taken in the.

stage containing the tube 4| would not add anything to the automaticvolume control voltage. The tube 4| is of the variable mu type so that alarge variation of the potential difference between the cathode and thegrid may be employed.

to give the desired range of volume control.

Even when a variable mu tube is employed, it is desirable to limit thegrid swing to avoid distortion. This is accomplished by impressing astepped-down signal on the grid of tube 4|, as previously described. Thesignal is then amplified up again to the desired value in the tube 4|and the transformer IOI, from which it is impressed upon the diode plate94, which acts as The transformer 99 includes a secondary winding I92which supplies potential to the diode plate 95 which is rectified andappears across the resistance I03. This direct current potential isutilized for automatic volume control, as previously described.

In this embodiment of the invention, the field of the loud speakercomprises two windings I04 and I05. The winding I04 is connected inseries with the plate voltage supply from the secondary of the powertransformer I5 through the rectifier tube IS. The winding I05 acts as achoke coil to filter the plate supply, as well as supplying part of theenergy to the speaker field. Only a part of the speaker field energy issupplied from the plate supply, the remainder for bringing the speakerto the proper sensitivity being supplied directly from the battery tothe coil I05. By properly proportioning these coils, the speaker fieldcan be employed as a choke coil and the proper speaker sensitivityattained with a vibrator of moderate output.

To avoid operating the vibrator without a load,

'it is desirable that the filaments of the tubes should have attainedtheir operating temperature before the vibrator is connected to thebattery. A thermostatic relay I06 fulfills this purpose. This relay isadapted to be operated by a heating winding I01 which is energized uponthe closing of the switch 38. The winding I01 is in parallel with thefilaments of the tubes and the current therefor is derived from thebattery. The thermostatic relay is proportioned to close the vibratorcircuit after the cathodes have attained operating temperature. Thethermostatic switch is preferably temperature compensated so. that itstime interval is not excessively affected by changes in atmospherictemperature.

The thermostatic relay serves both as a delayed switch and as a remotelycontrolled relay. The vibrator current does not pass through cable 21,thus reducing the liability of the introduction of undesirableelectrical disturbances into the amplifier tubes, and also avoiding thelarger conductors or higher voltage drop which would be occasioned by ahigher current through the cable.

The battery cable I08 comprisesthree leads I09. H0 and II I, surroundedby a shield I I2, one end of which connects to the chassis of the mainunit, and the other to the grounded terminal of the battery. Theconductor I09 is connected to the ungrounded terminal of the battery andleads to the switch 38 for the filament and heating element I01 supply.Conductor H0 is connected to the positive terminal of the battery andleads to one contact of the thermostatic relay I06, through which it isconnected in parallel through the primary winding of the transformer 15and vibrator 14 on the one hand, and through coil I05 on the other hand,to conductor III which is connected to the negative terminal of thebattery. In Fig. 2, I have shown the negative terminal of the battery tobe grounded.

Should the automobile be one in which the positive terminal is grounded,then shield H2 and conductor IIO should be connected to the positiveterminal of the battery, and conductors I09 and II I should be connectedto the negative terminal of the battery. It is to be noted that thishook-up follows the nomenclature of the preceding paragraph, accordingto which shield H2 is grounded and conductor I09 is connected to theungrounded terminal, and lead II is connected to the positive terminal,while lead III is connected to the negative terminal.

The operation of this embodiment will readily be understood from theforegoing description and its similarity to the embodiment of theinvention first described. It will readily be understood that when theswitch 38 is closed, the filaments begin to light up and the element I01begins to heat. By the time the filaments have attained their operatingtemperature, the thermostatic switch I06 has closed, completing thecircuit through the vibrator I4 and the primary of the 'shown in Figs. 1and 2'.

plate supply transformer 15, as well as through field coil I05. Tuningis efiected by means of the gang of condensers 49, 5| and 59, and manualvolume control is efiected by means of rheostat 63, in the mannerdescribed above.

For the satisfactory transfer of signal energy from the control unit tothe main unit, it is desired to employ means for minimizing loss orattenuation through the cable. In Figs. 6, 7, 8, and 9 are shown fourcircuits which may advantageously be used to attain this result undervarious conditions. The circuitshown in Fig. 6 is employed in theembodiments of the invention The common advantageous feature of allthese circuits is that the voltage difference between the conductorswithin the cable is substantially lower than the voltage across thecircuits in the control and main units, to which the conductors connector to which they are coupled. This low voltage difierence reduces theattenuation or loss through the capacity of the conductors in the cable.However, as a high voltage is desired for the input to the amplifier inthe main unit, the voltage should again be raised at the main unit endof the cable. The ratio of the voltage in the control unit and the mainunit to that in the cable should be great enough to avoid undue lossesthrough the capacity of the cable, but not so great as to cause undueresistance losses, resulting from very high currents flowing throughthese conductors.

The choice of the circuit to be used in a given set is dependent uponseveral factors, such as cost, permissible variation of characteristics,the

degree of selectivity desired, the tubes employed, the characteristicsof the cable, etc.

Where the capacity of the conductors of the cable is small, thestructure of Fig. 8 may be employed. The structure of Fig. 9 is suitablewith a cable of substantially fixed capacity. This permits of verysimple coils in the output of the control unit and the input of the mainunit. The structure of Fig. 6 permits of large capacity in the cablewhich does not have to be of a particularly exact value. The structureof Fig. '7 is highly advantageous when a high degree of selectivity isdesired.

Fig. 8 embodies direct coupling; Fig. 9, capacity coupling; Fig. 6,inductive coupling; and Fig. 7, coupling by means of a tuned linkcircuit.

Minimum losses or attenuation are obtained when the reactance at theintermediate frequency connected to one end of the cable is equal to thereactance connected to the other end of the cable, the value of thisreactance being determined by the electrical characteristics of thecable. For minimum losses the values of the various elements are soselected that if the cable is out at any point, the reactance at theintermediate frequency looking into the cable on one side of the cut isequal to the reactance looking into the cable on the other side of thecut, but if the reactance in the first case is capacitive, the reactancein the second case must be inductive, and vice Versa.

In the diagram shown in Fig. 6, the windings 53 and 56 have theircoefiicient of coupling as high as possible, likewise the windings 68and 10. The step down of voltage between windings 53 and 56 and the stepup between windings 69 and 10 are preferably of substantially similarmagnitude. In actual practice I have obtained excellent results with acircuit with a step down of times and a step up of 25 times, using atube of type R. C. A. 236 at 28 and a tube of type R. C. A. 239 at 39.As a result of the high step down, the capacity between the conductors6? and 68, illustrated as a phantom capacity at H3, is not critical andmay vary within considerable limits without greatly affecting the tuningof the circuits including the winding 53 and winding 10.

In the diagram shown in Fig. 7, the step down from winding 53 to winding56, and the step up from winding 69 to winding is lower than in the caseof Fig. 6, the number of turns in windings 56 and 69 being suitablyincreased to attain that result. In this case, the inductances ofwindings 56 and 69 are so considerable that they and the conductors 61and 68 connecting them constitute a link circuit which must be tuned tothe intermediate frequency to give best results. Such tuning is highlyadvantageous in that it enables a very high degree of selectivity to beattained, since it provides the added selectivity of an additional tunedcircuit without additional parts. The tuning of this circuit requires acapacity between the conductors 61 and 68, which capacity is shown inphantom at H4, to have a definite value.

Thus, in the case shown in Fig. 6, the length of the cable is immaterialwithin considerable limits, but in the case of Fig. 7, the length of thecable is important for best results, and if any considerable deviationfrom the optimum is attempted, correction of the capacity should be madein some manner, as, for example, providing a condenser between the leads6'! and 68 at either end, or by selecting a cable of more suitablecapacity characteristics.

The structure diagrammatically shown in Fig. 8, in which direct couplingis employed, is particularly suitable for use with tubes 28 and 39 oflow impedance. In this arrangement coils 53 and 10 are connected by theleads 81 and 68, condensers H5 and H6 being provided in the lead 68,that is, the ungrounded lead. The condensers H5 and H6 are of largecapacity relative to the capacity of the cable, as indicated in phantomat H1. As the capacity of the cable is small, relative to the capacitiesH5 and H6, the system is independent to a considerable degree of thecapacity between the leads 61 and 68.

The structure diagrammatically shown in Fig. 9, in which capacitivecoupling is employed, is adapted for use when the tubes 28 and 39 are ofhigh impedance. The windings 53 and 10 are of high inductance and thecondensers H8 and H9 are of relatively low capacity relative to thatbetween the leads 6'! and 68, which is indicated at I20. Under thesecircumstances two separate circuits are formed with the capacity I20common to both and forming the coupling link therebetween. Here thecapacity of the cable must have a relatively definite value incomparison with the capacity Ill of Fig. 8.

The voltage between the conductors 61 and 68 is maintained low in thecircuits shown in Figs. 6, 7, 8 and 9, and attenuation of the signalcurrents in passing through the cable is thereby substantiallyminimized. In the structures of Figs. 6 and 7, this low voltage relationis secured by stepping down the voltage across the winding 53 to a lowervoltage across the coil 56. In the structure of Fig. 8 the potentialdrop across the winding 53 is substantially equal to the potential dropacross condenser I I5, and the potential drop across the winding 70 issubstantially equal to the potential drop across condenser H6.

In the structure of Fig. 9, a similar relation exists between thewinding 53 and condenser H8 on the one hand, and between winding Ill andcondenser US on the other hand. In both cases the potential of .theleads 6] and 68 is-substantially equal.

It is not intended tolimit the invention to automobile radio receivers,since it may be applied to. home sets and indeed to any manner of setemploying a remote control. In the embodiment of the inventionillustratedin Fig. 10, the main unit is substantially similar to thatshown in Fig. 2. The principal difference is that the automatic volumecontrol is applied to the tube 28 in the remote unit, as well as tubesin the main unit. By this ex pedient the tube 40 may be omitted from themain unit while maintaining an ample amount of automatic volume control.For the sake of simplicity, I have shown the power supply system of Fig.1 in this embodiment.

The automatic volume control voltage is rectified at the plate 95 of thetube 43 and is applied to the grids of the tubes 39 and 4| in the mannerdescribed above with respect to the embodiment shown in Fig. 2. That is,the whole automatic volume control voltage is applied to the grid oftube 39 and a part thereof, determined by the resistances I2I, I22 andI23, is applied to the grids of tube II and the tub-e 28 in thecontrolunit, by means of the lead I24, an additional conductor which passesthrough the cable 21.

The tube 28 in the remote control unit is a six-element tube comprisinga cathode I25, plate I26, control grid I27 and screen I28, an oscillatorgrid I29, and an oscillator plate I30. The oscillator grid I29 andoscillator plate I31], together with the cathode I25, serve asoscillator elements independent of the control grid I21, so that thebias of the grid I21 can be varied to obtain automatic volume controlwithout interfering with the local oscillation. The electron streamreaching the plate I26 is afiected both by the local oscillationfrequency and the signal frequency on the grid I21 in such a way thatthe intermediate frequency appears across the coil 53 and is transferredto the coil 56. The intermediate frequency passes from the coil 56through conductor 68 to the input of the tube 39.

It is not intended to be limited to this particular type of tube, sinceother tubes may be employed, if desired, provided the bias of thecontrol grid can be sufficiently varied without impairing the localoscillation.

Although the invention has been described in connection with thespecific details of preferred embodiments thereof, it must be understoodthat such details are not intended to be limitative of the invention,except insofar as set forth in the following claims.

Having thus described claim and desire to secure the United States is1 1. In a radio receiver, in combination, a metal base, a plurality ofthermionic tubes having plates and filaments, each of said filamentsbeing provided with a pair of terminals, a continuously vibratingcircuit interrupter having an inductance element and two contacts, ametal shield enclosing said interrupter, a transformer having a primarywinding and a secondary winding arrangedto transform low voltagealternating current into high voltage alternating current, a rectifiercircuit connected across said secondmy invention, what I by LettersPatent of a'ry winding, said rectifier circuit acting to change the highvoltage alternating current into high voltage direct current, means fordelivering'said high voltage direct current to said plates, saidthermionic tubes, shielded interrupter, transformer, and rectifier beingcarried by said base, a metal housing enclosing them, one terminal ofeach of said filaments,one of said interruptercontacts and its shieldbeing grounded to said metal base which forms'the common ground for saidradio receiver, a low voltage battery external to said housing having apair of terminals, means for grounding one of said pair of batteryterminals to a ground external to said receiver, conductor meansconnecting the base of said radio receiver to the grounded terminal ofthe battery, a second conductor means connecting the ungrounded terminalof the battery to said filaments, and a third conductor means connectingthe other of said two interrupter contacts to said second conductormeans, said third conductor means including said interrupter inductanceelement and the primary of said transformer in series.

2. In a radio receiver with self-contained power supply comprising ametal base carrying the elements of the receiver and power supply andforming a common ground for them, in combination, thermionic tubesprovided with filaments each of which is provided with a pair ofterminals, means for grounding one of each of said pair of terminals tosaid base, a vibrating interrupter having a pair of contacts and adriving coil, one of said contacts being grounded to said base, agrounded metal shield enclosing said vibrating interrupter, atransformer having a primary Winding and a secondary winding, meansincluding a rectifier intermediate said secondary winding and saidplates for supplying plate current to said receiver, a low voltagebattery separated from said metal base, said battery having a pair ofterminals, means for connecting one of said battery terminals to thebase and to an external ground other than said metal base, a conductormeans connecting the ungrounded terminal of each filament to theungrounded terminal of the battery, and a second conductor meansconnecting the ungrounded interrupter contact to said first namedconductor means, said second conductor means including said driving coiland the primary winding of said transformer in series.

3. In a radio receiver with self-contained power supply comprising ametal base carrying the elements of the receiver and power supply andforming a common ground for them, in combination, thermionic tubeshaving filaments each of which is provided with a pair of terminals, oneterminal of each pair being grounded to said base, a vibratinginterrupter having a pair of contacts and a driving coil, means forgrounding one of said contacts to said base, a metal shield enclosingsaid vibrating interrupter, a transformer having a primary winding and asecondary winding, means, including a rectifier, interposed between thesecondary winding of said transformer and said tubes for supplying platecurrent to saidreceiver, a low voltage battery external to said base,said battery having a pair of terminals, means for grounding one of saidbattery terminals to a ground external to said base, conductor meansconnecting the base of said radio receiver to the grounded terminal ofthe battery, a second conductor means connecting the ungrounded terminalof the battery to the ungrounded terminals of said filaments, a thirdconductor means connecting the ungrounded interrupter contact to thesecond conductor means, said third conductor means including saiddriving coil and said primary winding in series, and a by-pass condenserconnected between said base and a point of the third conductor meanswhich is common to said primary Winding and said driving coil.

4. In a radio receiver with self-contained power supply comprising ametal base carrying the elements of the receiver and power supply andforming a common ground for them, in combination, thermionic tubeshaving filaments each of which is provided with a pair of terminals,means for grounding one terminal of each pair of terminals to said base,a vibrating interrupter having contact elements and a driving coil, oneof said contact elements being grounded to said base, a transformerhaving a primary winding and a secondary winding, means including arectifier connected between said secondary winding and said tubes forsupplying plate current to said receiver, a battery having a pair ofterminals, means for connecting one of said battery terminals to saidmetal base and to a ground external to said base, conductor meansconnecting the ungrounded terminal of the battery to the ungroundedterminals of said filaments, a second conductor means connecting anotherof said interrupter contact elements to first said conductor means,through said primary, inductance means including said driving coil inseries with said primary in said last named conductor means, a by-passcondenser connected between said grounded interrupter contact elementand a point of said second conductor means which is common to saidprimary and said inductance means, and grounded metal shielding meansshielding said interrupter contacts, said inductance and said condenser.

5. In a radio receiver with self-contained power supply comprising ametal base carrying the elements of the receiver and power supply andforming a common ground for them, in combination, a loud speakerconnected to said receiver, said loud speaker having a low voltage fieldwinding provided with a pair of terminals, 2. housing for said speakerarranged to cover said elements on said base, means for grounding oneterminal of said field winding to said base, thermionic tubes havingfilaments each of which is provided with a pair of terminals, means forgrounding one terminal of each of said pairs of filament terminals tosaid base, a vibrating interrupter having a driving coil and a pair ofcontacts, means for grounding one of said interrupter contacts to saidbase, a metal shield'enclosing said vibrating interrupter, a transformerhaving a primary winding and a secondary winding, means including arectifier, interposed between said transformer and said tubes forsupplying plate current to said receiver, a battery having a pair ofterminals, means for grounding one of the battery terminals to saidmetal base and to an external ground other than said base, conductormeans connecting the ungrounded terminal of the battery to theungrounded filament terminals and to the ungrounded field windingterminal, a second conductor means connecting the ungrounded interruptercontact through said primary and said driving coil in series to thefirst said conductor means.

6. In a radio receiver with self-contained power supply comprising ametal base carrying the elements of the receiver and power supply andforming a common ground for them, in combi nation, thenmionic tubeshaving filaments each of which is provided with a pair of terminals,means for grounding one terminal of each pair to said base, a vibratinginterrupter having a pair of contacts, means for grounding one of saidcontacts to said base, a metal shield enclosing said interrupter, atransformer having a primary winding and a secondary winding, meansincluding a rectifier circuit connected between said transformer andsaid tubes for supplying plate current to said receiver, a batteryhaving a pair of terminals, means for connecting one of said batteryterminals to said base and to a ground external to said receiver,conductor means connecting the ungrounded interrupter contact to oneterminal of said primary winding, and means connecting the otherterminal of said primary winding to the ungrounded terminal of thebattery and the ungrounded terminal of each filament.

7. In a radio receiver with self-contained power supply comprising ametal base carrying the elements of the receiver and power supply andforming a common ground for them, in combination, thermionic tubeshaving filaments each of which is provided with a pair of terminals,means for grounding one terminal of each pair to said base, a vibratinginterrupter having a pair of contacts, means for grounding one of saidcontacts to said base, a metal shield grounded to the base and enclosingsaid interrupter, a transformer having a primary winding and a secondarywinding, means including a rectifier, interposed between saidtransformer and said tubes for supplying plate current to said tubes, abattery having a pair of terminals, means for grounding one of saidbattery terminals to said metal base and to a ground external to saidbase, conductor means connecting the ungrounded interrupter contactthrough said primary to the ungrounded terminal of said battery and theungrounded terminals of said filaments, and means connected with saidconductor cooperating with said primary to form a progressive filter forpreventing high frequency disturbance originating at said contacts frompassing into the ungrounded conductors leading to said battery and saidfilaments.

8. In a radio receiver having a ground member to which various of itselements are connected, in combination, thermionic tubes havingfilaments each filament being provided with a pair of terminals, meansfor connecting one terminal of each of said pairs of terminals to saidground member, a vibrating interrupter having a driving coil and a pairof cooperating contacts, means for connecting one of said pair ofcontacts to said ground member, a metal shield connected to said groundmember and enclosing said interrupter, a transformer having a primarywinding and a secondary winding, means including a rectifier interposedbetween said transformer and said tubes for supplying plate current tosaid receiver, a battery having one terminal connected to said groundmember and to an external ground, and another terminal connected to theungrounded terminals of the filaments, a second conductor meansconnecting the ungrounded interrupter contact through said driving coiland said primary in series to said ungrounded terminals of thefilaments, said driving coil being connected in said second conductormeans close to said primary,

9. In a radio receiver, in combination, a metal base, a plurality ofthermionic tubes having plates and filaments each of said filamentshaving a pair of terminals, a continuously vibrating circuit interrupterincluding a pair of cooperating contacts, a metal shield enclosing saidinterrupter, a transformer having a primary winding and a secondarywinding, a rectifier connected between said transformer and said tubesfor receiving energy from said secondary winding and delivering highvoltage direct current to said plates, said thermionic tubes, shieldedinterrupter, transformer, and rectifier being arranged in compactrelation and carried by said base, a metal housing enclosing them, a lowvoltage battery having a pair of terminals, said battery being mountedexternal to said housing, means for grounding one terminal of saidbattery to a ground external to said metal base, one terminal of each ofsaid filaments, one contact of said interrupter, and its shield beinggrounded to said metal base, a common ground conductor connecting themetal base to the grounded terminal of said battery, conductor meansconnecting the ungrounded ends of the filaments to one end of thetransformer primary Winding, means for connecting the other end of theprimary winding to the other terminal of said interrupter, and a commonungrounded conductor connecting said last named conductor means to theungrounded terminal of said battery, said common conductor carrying bothfilaments and interrupter current.

10. In a radio receiver, in combination, a metal base, a plurality ofthermionic tubes having plates and filaments, each of said filamentsbeing provided with a pair of terminals, 2. speaker having a field coilprovided with a pair of terminals, a continuously vibrating circuitinterrupter having a pair of cooperating contacts, a metal shieldenclosing said interrupter, a transformer having a primary winding and asecondary winding, a rectifier circuit connected between saidtransformer and said tubes for receiving energy from said secondarywinding and delivering high voltage direct current to said plates, saidthermionic tubes, shielded interrupter, transformer and rectifier beingarranged in compact relation and carried by said base, a metal housingenclosing them, said speaker being located within said housing, a lowvoltage battery external to said housing, said battery being providedwith a pair of terminals, means for connecting one of said batteryterminals to a ground external to the metal base, one terminal of eachof said filaments, one terminal of said speaker field coil, and onecontact of said interrupter and its shield being grounded to said metalbase, a common ground conductor connecting the metal base to thegrounded terminal of said battery, conductor means connecting theungrounded terminal of the filaments, and the ungrounded terminal of thespeaker field coil to one end of the transformer primary winding, theother end of said primary winding being connected to the other contactof said interrupter, a common ungrounded conductor connecting said lastnamed conductor means to the ungrounded terminal of said battery, and aswitch in said common ungrounded conductor, said common conductorcarrying both filament and interrupter current.

11. In a radio receiver, in combination, a metal base, a plurality ofthermionic tubes having plates and filaments, a continuously vibratingcircuit interrupter having two cooperating contacts and a driving coil,a metal shield enclosing said interrupter, a transformer having aprimary Winding and a secondary winding, a rectifier connected to saidsecondary Winding for receiving energy from said winding and producinghigh voltage direct current therefrom, means for delivering the highvoltage direct current to said plates, said thermionic tubes, shieldedinterrupter, transformer, and rectifier being carried by said base, ametal housing enclosing them, one terminal of each of said filaments,one of said interrupter contacts and the interrupter shield beinggrounded to said metal base which forms the common ground for said radioreceiver, a pair of terminals one of which is grounded to a groundexternal to said receiver, said pair of terminals being adapted to haveconnected between them a low voltage battery, conductor means connectingthe base of said radio receiver to the grounded one of said pair ofterminals, a second conductor means connecting the other of theungrounded terminals of said pair of terminals to said filaments, athird conductor means connecting the other of said interrupter contactsthrough the driving coil and the primary of said transformer to thesecond conductor means, said driving coil and primary winding havingsufficient inductance to present a high impedance to the passage of highfrequency disturbances originating in the vibrating circuit interrupterto said second conductor means.

12. In a radio receiver, in combination, a metal base forming a groundfor said receiver, a plurality of thermionic tubes having plates andfilaments each of said filaments being provided with a pair ofterminals, a continuously vibrating circuit interrupter having a pair ofcooperating contacts and a driving coil, a metal shield enclosing saidinterrupter, a transformer provided with a primary winding and asecondary winding, a rectifier and filter circuit interposed betweensaid secondary winding and said plates, said thermionic\ tubes, shieldedinterrupter, transformer, and rectifier being carried by said base, ahousing enclosing them, means for connecting one terminal of each ofsaid filaments, one of the interrupter contacts and the interruptershield to said metal base, a pair of source terminals, means forconnecting one of said source terminals to a ground external to saidreceiver, conductor means connecting the base of said radio receiver tothe grounded source terminal, a second conductor means, including highfrequency impeding means, connecting the other source terminal to theungrounded terminals of said filaments, means including said drivingcoil and said primary winding in series, for connecting the other ofsaid interrupter contacts to said second conductor means, said drivingcoil and primary winding presenting a high impedance to the passage ofhigh frequency disturbances originating in the vibrating circuitinterrupter to said second conductor means.

13. In signalling apparatus, a metal base forming a common ground forsaid apparatus, a plurality of thermionic tubes having plates andfilaments, each of said filaments being provided with a pair ofterminals, a vibrating circuit interrupter including a driving coil anda pair of cooperating contacts, a metal shield enclosing said circuitinterrupter, a transformer having a primary winding and a secondarywinding arranged to transform low voltage alternating current into highvoltage alternating current, a rectifier circuit connected across thesecondary Winding and arranged to change the high voltage alternatingcurrent into high voltage direct current, means for delivering the highvoltage direct current to the plates of said tubes, said thermionictubes, shielded interrupter, transformer and rectifier circuit beingcarried by said base, a metal housing enclosing them, means forgrounding one terminal of each of said filaments and said interruptershield to said metal base, a low voltage battery external to saidhousing and having a pair of terminals, means for grounding one of saidbattery terminals to a ground external to said receiver, conductor meansconnecting the grounded terminal of the battery to the base of saidradio receiver, a second conductor means connecting the ungroundedterminal of said battery to the ungrounded terminals of said filamentsand a third conductor means connected between said metal base and saidsecond conductor, said third conductor means including the driving coilof said circuit interrupter and the primary winding of said transformerin series, said driving coil being adapted to impede the flow ofdisturbing energy generated by said circuit interrupter to said secondconductor means.

EDWARD F. ANDREWS.

Jan. 6, 1942. N. A. WHITTAKER ELECTRIC PARKING METER Filed Dec. 9, 19402 Sheets-Sheet 1 3nventor Vorman .fl. PWzz'tta/ta' (Ittorneg

